Motor control system and method for skipping resonant operating  frequencies

ABSTRACT

A system and method of avoiding hunting behavior by a motor around disallowed speed ranges. A sensor or sensorless method determines the motor&#39;s actual speed. A memory contains lower and upper speed values that define a disallowed range. A control unit determines whether the motor is operating under a limiting condition and engaged in hunting behavior by determining whether the motor is repeatedly moving between an actual speed that is within the disallowed range and an actual speed that is at or below the lower speed value during a first period, and if so, sets a temporary speed limit for the motor at the lower speed value for a second period. The first period may be the time required for the motor to change its actual speed a few times and thereby confirm hunting behavior. The second period may be sufficiently long that the limiting condition may have changed.

FIELD

The present invention relates to systems and methods for controlling theoperation of electric motors.

BACKGROUND

The operation of electric motors can be characterized by their inputfrequencies (measured in Hertz (Hz)) and corresponding output speeds(measured in revolutions per minute (RPM)). The input frequency to avariable speed electric motor can be varied to change the output speed,which allows the same electric motor to be used with, e.g., differentfan blades rated at different speeds and load points.

Fan blades may experience resonance at certain RPM. This resonance canbe amplified into mechanical vibrations which may cause damage to thefan blades as well as unwanted noise. One solution is to avoid the RPMrange associated with resonance by not allowing the electric motor tooperate within that range. However, the electric motor may require anRPM within the disallowed RPM range in order to maintain a certainamount of power or torque, in which case disallowing the required RPMmay result in even more noise or in the electric motor exhibiting“hunting” behavior, i.e., repeatedly jumping back and forth over thedisallowed RPM range between a higher RPM that is not allowed and alower RPM that is too slow. More specifically, a motor controller maycommand the electric motor to operate at a desired RPM that is justabove the disallowed RPM range. However, load and/or temperature effectsmay prevent the electric motor from achieving the desired RPM, and maycause it to achieve an actual RPM that is within the disallowed RPMrange, which then causes it to drop to an allowed actual RPM that isjust below the disallowed RPM range. When the motor controller sensesthat the electric motor's actual RPM is substantially below the desiredRPM, it commands the electric motor to return to the desired RPM whichthe electric motor cannot achieve. This cycle of jumping back and fortharound the disallowed RPM range continues until the limiting operatingconditions change so that the electric motor is able to achieve thedesired RPM.

This background discussion is intended to provide information related tothe present invention which is not necessarily prior art.

SUMMARY

Embodiments of the present invention solve the above-described and otherproblems and limitations by providing improved avoidance of one or moredisallowed RPM ranges while still maintaining proper control over anelectric motor operating in a limiting (e.g., power- ortemperature-limiting) mode, including avoiding hunting behavior aroundthe disallowed RPM ranges.

An electric motor system constructed in accordance with an embodiment ofthe present invention may broadly comprise an electric motor having ashaft for driving a load, and a motor control subsystem operable tocontrol operation of the electric motor. The motor control subsystem mayinclude a speed determiner operable to measure, estimate, or otherwisedetermine an actual speed value of the electric motor, a memory elementcontaining a first lower speed value and a first upper speed value,which together define a first disallowed speed range for the electricmotor, and a control unit in electrical communication with the speeddeterminer and the memory element. The control unit may be operable tocalculate a desired speed value for the electric motor, wherein thedesired speed value is not within the first disallowed speed range, andto generate and send an electrical signal to cause the electric motor toattempt to achieve the desired speed value, receive the determinedactual speed value of the electric motor from the speed determiner, anddetermine whether the electric motor is unable to achieve the desiredspeed value due to a limiting condition and is repeatedly changingbetween a first actual speed value that is at or below the first lowerspeed value and a second actual speed value that is within the firstdisallowed speed range over a first predetermined period of time (i.e.,that the electric motor is engaged in hunting behavior). If the controlunit determines that the electric motor is engaged in such huntingbehavior, the control unit may set a temporary speed limit for theelectric motor at the first lower speed value for a second predeterminedperiod of time. At the end of the second predetermined period of time,the control unit may remove the temporary speed limit to determinewhether the limiting condition still exists.

In various implementations of this embodiment, the electric motor systemmay further include any one or more of the following additionalfeatures. The electric motor may be a three-phase, permanent magnetelectric motor. The load may be a fan component of a heating andair-conditioning unit. The first predetermined time may be approximatelybetween 20 seconds and 40 seconds, or approximately the time requiredfor the electric motor to change between the first actual speed and thesecond actual speed between one time and three times. The secondpredetermined time may be approximately between 20 minutes and 40minutes. The memory element may further contain a second lower speedvalue and a second upper speed value which together define a seconddisallowed speed range. In this case, the control unit may be operableto determine whether the electric motor is unable to achieve the desiredspeed value due to a limiting condition and is repeatedly changingbetween the first actual speed value that is within the seconddisallowed speed range and the second actual speed value that is at orbelow the second lower speed value over the first predetermined periodof time, and if so, set the temporary speed limit for the electric motorat the second lower speed value for the second predetermined period oftime.

The first disallowed speed range may be associated with a first flag inthe memory element, and if the first flag is not set then the controlunit may ignore the first disallowed speed range. The second disallowedspeed range may also be associated with the first flag in the memoryelement, and if the first flag is set then the control unit may ignorethe second disallowed speed range. Alternatively, the first disallowedspeed range may be associated with a first flag in the memory element,and if the first flag is not set then the control unit may ignore thefirst disallowed speed range. The second disallowed speed range may beassociated with a different second flag in the memory element, and ifthe second flag is not set then the control unit may ignore the seconddisallowed speed range.

Additionally, each of these implementations and embodiments may bealternatively characterized as methods based on their functionalities.

This summary is not intended to identify essential features of thepresent invention, and is not intended to be used to limit the scope ofthe claims. These and other aspects of the present invention aredescribed below in greater detail.

DRAWINGS

Embodiments of the present invention are described in detail below withreference to the attached drawing figures, wherein:

FIG. 1 is a schematic diagram of an electric motor system of the presentinvention;

FIG. 2 is a block diagram of components of a motor control subsystem ofthe electric motor system of FIG. 1;

FIG. 3 is a plot of input voltage that references a speed command to anelectric motor component of the motor control system of FIG. 1 andcorresponding output speed of the electric motor component;

FIG. 4 is a plot of a speed command signal from the motor controlsubsystem and an actual speed of the electric motor of the electricmotor system of FIG. 1 over time;

FIG. 5 is a flow diagram of steps involved in the operation of theelectric motor system of FIG. 1;

FIG. 6 is a flow diagram of additional steps involved in the operationof a first implementation of the electric motor system of FIG. 1; and

FIG. 7 is a flow diagram of additional steps involved in the operationof a second implementation of the electric motor system of FIG. 1.

The figures are not intended to limit the present invention to thespecific embodiments they depict. The drawings are not necessarily toscale.

DETAILED DESCRIPTION

The following detailed description of embodiments of the inventionreferences the accompanying figures. The embodiments are intended todescribe aspects of the invention in sufficient detail to enable thosewith ordinary skill in the art to practice the invention. Otherembodiments may be utilized and changes may be made without departingfrom the scope of the claims. The following description is, therefore,not limiting. The scope of the present invention is defined only by theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

In this description, references to “one embodiment”, “an embodiment”, or“embodiments” mean that the feature or features referred to are includedin at least one embodiment of the invention. Separate references to “oneembodiment”, “an embodiment”, or “embodiments” in this description donot necessarily refer to the same embodiment and are not mutuallyexclusive unless so stated. Specifically, a feature, structure, act,etc. described in one embodiment may also be included in otherembodiments, but is not necessarily included. Thus, particularimplementations of the present invention can include a variety ofcombinations and/or integrations of the embodiments described herein.

Broadly characterized, the present invention provides improved avoidanceof one or more disallowed RPM ranges while still maintaining propercontrol over an electric motor operating in a limiting (e.g., power- ortemperature-limiting) mode, including avoiding hunting behavior aroundthe disallowed RPM ranges. Referring to the figures, an electric motorsystem 10 constructed in accordance with the present invention is shown.Referring to FIGS. 1 and 2, in an embodiment of the present invention,the electric motor system 10 may broadly comprise an electric motor 12;a power source 14; and a motor control subsystem 16 including a speedsensor 20, one or more memory elements 22, and a control unit 24.

The electric motor 12 may be any suitable variable speed electric motordriving any appropriate load 30 via a shaft 32. The load 30 may be, forexample, a fan or a pump which may be part of a heating andair-conditioning unit, such as a commercial blower, or an appliance,such as a washing machine or a clothes dryer, which may includeadditional electrical or mechanical components not described herein. Inone implementation, the electric motor 12 may be a variable speed, threephase, permanent magnet electric motor driving a condenser fan 30 in aheating and air-conditioning unit. The power source 14 may be anysuitable residential, commercial, or other source of power.

The motor control subsystem 16 may be broadly operable to controloperation of the electric motor 12, including receiving power from thepower source 14 and generating a driving waveform to drive the electricmotor 12. The speed sensor 20 may be operable to measure or otherwisedetermine an actual speed value of the electric motor 12. In oneimplementation, the speed sensor 20 may be located on the shaft 32 ofthe electric motor 12, and may take any suitable form, includingmechanical, electrical (e.g., a Hall effect sensor), or optical.Alternatively, the speed sensor may be replaced by a sensorless methodof estimating or otherwise determining the speed of the electric motor12. Referring also to FIG. 3, the one or more memory elements 22 maycontain a first lower speed value 40 and a first upper speed value 42,which together define a first disallowed speed range 44 for the electricmotor 12. The one or more memory elements 20 may take any suitable form,including one or more electrically erasable programmable read onlymemories (EEPROMs).

The control unit 24 is in electrical communication with the speed sensor20 and the one or more memory elements 22, and operable to receiveinputs therefrom and to generate and send command signals based thereonfor controlling operation of the electric motor 12. The control unit 24may take any suitable form, including only or primarily hardwarecomponents, only or primarily software components, or a combination ofhardware and software components.

In particular, referring also to FIG. 4, the control unit 24 may beoperable to calculate a desired speed value for the electric motor 12,wherein the desired speed value is not within the disallowed speedrange, and to generate and send a speed command signal 46 to cause theelectric motor 12 to attempt to achieve the desired speed value. Thecontrol unit 24 may be further operable to receive the measured actualspeed value 48 of the electric motor 12 from the speed sensor 20, and todetermine whether the electric motor 12 is unable to achieve the desiredspeed value due to a limiting condition and is engaging in huntingbehavior, i.e., repeatedly changing between a first actual speed valuethat is at or below the first lower speed value and a second actualspeed value that is within the first disallowed speed range 44 over afirst predetermined period of time 50. If the electric motor 12 isengaging in hunting behavior, the control unit 24 may be furtheroperable to set a temporary speed limit for the electric motor 12 at thefirst lower speed value 40 for a second predetermined period of time 52.The control unit 24 may be further operable to remove the temporaryspeed limit at the end of the second predetermined period of time 52 inorder to determine whether the limiting condition still exists (asevidenced by the electric motor 12 continuing to engage in huntingbehavior), and if so, repeat the foregoing process.

As mentioned, the limiting condition may be, e.g., power or temperatureeffects which prevent the electric motor 12 from achieving the desiredspeed value. The first predetermined period of time 50 may beapproximately between 20 seconds and 40 seconds, or approximately 30seconds, or approximately the time required for the electric motor 12 tochange between the first actual speed and the second actual speedbetween one time and three times (i.e., sufficient time to confirm thatthe electric motor 12 is engaging in hunting behavior). The secondpredetermined period of time 52 may be approximately between 20 minutesand 40 minutes, or 30 minutes (i.e., sufficient time in which a limitingcondition might change).

In one implementation, the electric motor system 10 may be operable toavoid multiple RPM ranges. For example, the one or more memory elements22 may further contain a second lower speed value 54 and a second upperspeed value 56 which together define a second disallowed speed range 58.In this implementation, the control unit 24 may be further operable todetermine whether the electric motor 12 is unable to achieve the desiredspeed value due to a limiting condition and is repeatedly changingbetween the first actual speed value that is within the seconddisallowed speed range 58 and the second actual speed value that is ator below the second lower speed value 54 over the first predeterminedperiod of time 50, and if so, set the temporary speed limit for theelectric motor 12 at the second lower speed value 54 for the secondpredetermined period of time 52. Thus, the additional disallowed RPMranges may be treated the same or similar to the first disallowed RPMrange.

Furthermore, when the electric motor system 10 is operable to avoidmultiple disallowed RPM ranges, an operator of the system 10 may beallowed to enable one or more of the RPM ranges 44,58 and disableothers, wherein the control unit 24 may ignore any disabled disallowedRPM ranges 44,58. For example, in a first implementation, the firstdisallowed speed range 44 may be associated with a first flag in thememory element 22, and if the first flag is not set then the controlunit 24 may ignore the first disallowed speed range 44, and the seconddisallowed speed range 58 may also associated with the same first flagin the memory element 22, and if the first flag is set then the controlunit 24 may ignore the second disallowed speed 58 range. In a secondimplementation, the first disallowed speed range 44 may be associatedwith a first flag in the memory element 22, and if the first flag is notset then the control unit 24 may ignore the first disallowed speed range44, and the second disallowed speed range 58 may be associated with itsown second flag in the memory element 22, and if the second flag is notset then the control unit 24 may ignore the second disallowed speedrange 58. For example, the first disallowed speed range 44 may be storedin EEPROM locations 52 and 54, and the second disallowed speed range 58may be stored in EEPROM locations 192 and 194. The disallowed speedranges 44,58 may be enabled or disabled by a high byte and a low byte inEEPROM location 190, wherein if the high byte in location 190 equals hA5then the first disallowed speed range 44 is disabled and ignored by thecontrol unit 24 and if the lower byte equals hA5 then the seconddisallowed speed range 58 is disabled and ignored.

In operation, an embodiment of the electric motor system 10 of thepresent invention may function substantially as follows. Referring toFIG. 5, the first disallowed speed range 44 for the electric motor 12 isdefined by storing in the memory element 22 the first lower speed value40 and the first upper speed value 42, as shown in step 100. The controlunit 24 calculates a desired speed value for the electric motor 12,wherein the desired speed value is not within the first disallowed speedrange 44, and the control unit 24 generates and sends an electricalspeed command signal to cause the electric motor 12 to attempt toachieve the desired speed value, as shown in step 102. The speed sensor20 measures the actual speed value 48 of the electric motor 12, as shownin step 104. The control unit 24 determines whether the electric motor12 is unable to achieve the desired speed value due to a limitingcondition and is repeatedly changing between a first actual speed valuethat is at or below the first lower speed value 40 to a second actualspeed value that is within the first disallowed speed range 44 (i.e., isengaged in hunting behavior) over the first predetermined period of time50, as shown in step 106. If the electric motor 12 is engaged in huntingbehavior, then the control unit 24 sets the temporary speed limit forthe electric motor 12 at the lower speed value 40 for the secondpredetermined period of time 52, as shown in step 108. The control unit24 removes the temporary speed limit at the end of the secondpredetermined period of time 52, as shown in step 110, to determinewhether the limiting condition still exists (i.e., whether the electricmotor 12 returns to hunting behavior, as shown in step 106). If theelectric motor 12 returns to hunting behavior after the secondpredetermined period of time 52, then the process repeats by returningto step 108.

A second (and subsequent) disallowed speed range 58 may be defined forthe electric motor by storing in the memory element 22 the second lowerspeed value 54 and a second upper speed value 56, as shown in step 200.The control unit 24 may treat this second disallowed speed range 58substantially similar to or the same as the first disallowed speed range44.

Referring also to FIGS. 6 and 7, the first disallowed speed range 44 maybe associated with the first flag in the memory element 22, and thesystem 10 may allow for setting the first flag, as shown in step 200.The control unit 24 may determine whether the first flag is set or not,as shown in step 202. If the first flag is not set, then the controlunit 24 may ignore the first disallowed speed range 44, as shown in step204, and if the first flag is set, then the control unit 24 may ignorethe second disallowed speed range 58, as shown in step 206.Alternatively, the first disallowed speed range 44 may be associatedwith the first flag in the memory element 22, and the system 10 mayallow for setting the first flag, as shown in step 300. Similarly, thesecond disallowed speed range may be associated with the second flag inthe memory element 22, and the system 10 may allow for setting thesecond flag, as shown in step 306. The control unit 24 may determinewhether the first flag is set, as shown in step 302, and if the firstflag is not set then the control unit may ignore the first disallowedspeed range 44, as shown in step 304. Similarly, the control unit 24 maydetermine whether the second flag is set, as shown in step 308, and ifthe second flag is not set then the control unit 24 may ignore thesecond disallowed speed range 58, as shown in step 310.

For example, if the control unit 24 has calculated and commanded adesired electric motor speed of940 RPM, but due to a limiting conditionthe electric motor 12 actually operates at 930 RPM, and a disallowed RPMrange has been established between 900 and 935 RPM such that theelectric motor 12 begins several cycles of hunting across the disallowedrange, then the control unit 24 may set the maximum RPM at 900 RPM for30 minutes. At the end of the 30 minute period, the control unit 24 mayreset the maximum RPM and reassert the command signal for 940 RPM. Ifthe electric motor 12 begins hunting again, then the process repeats.

It will be understood that references in the foregoing description to“avoiding” or “skipping” a disallowed speed range 44,58 mean notcommanding the electric motor 12 to achieve and hold a particular speedvalue within the disallowed speed range and, when necessary, movingrelatively quickly through those disallowed speed ranges 44,58.

Thus, the present invention provides advantages over the prior art,including that it provides improved avoidance of one or more disallowedRPM ranges 44,58 while still maintaining proper control over theelectric motor 12 operating in a limiting (e.g., power- ortemperature-limiting) mode, including avoiding hunting behavior aroundthe disallowed ranges 44,58.

Although the invention has been described with reference to the one ormore embodiments illustrated in the figures, it is understood thatequivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims.

Having thus described one or more embodiments of the invention, what isclaimed as new and desired to be protected by Letters Patent includesthe following:

1. An electric motor system comprising: an electric motor having a shaftfor driving a load; and a motor control subsystem operable to controloperation of the electric motor, the motor control subsystem including—a speed determiner operable to determine an actual speed value of theelectric motor, a memory element containing a first lower speed valueand a first upper speed value which together define a first disallowedspeed range for the electric motor, and a control unit in electricalcommunication with the speed determiner and the memory element, andoperable to— calculate a desired speed value for the electric motor,wherein the desired speed value is not within the first disallowed speedrange, and to generate and send an electrical signal to cause theelectric motor to attempt to achieve the desired speed value, receivethe determined actual speed value of the electric motor from the speeddeterminer, determine whether the electric motor is unable to achievethe desired speed value due to a limiting condition and is repeatedlychanging between a first actual speed value that is at or below thefirst lower speed value and a second actual speed value that is withinthe first disallowed speed range over a first predetermined period oftime, if so, set a temporary speed limit for the electric motor at thefirst lower speed value for a second predetermined period of time, andat the end of the second predetermined period of time, remove thetemporary speed limit.
 2. The electric motor system as set forth inclaim 1, wherein the electric motor is a three-phase permanent magnetelectric motor.
 3. The electric motor system as set forth in claim 1,wherein the load is a fan component of a heating and air-conditioningunit.
 4. The electric motor system as set forth in claim 1, wherein thefirst predetermined time is approximately between 20 seconds and 40seconds.
 5. The electric motor system as set forth in claim 1, whereinthe first predetermined time is approximately the time required for theelectric motor to change between the first actual speed and the secondactual speed between one time and three times.
 6. The electric motorsystem as set forth in claim 1, wherein the second predetermined time isapproximately between 20 minutes and 40 minutes.
 7. The electric motorsystem as set forth in claim 1, wherein the memory element furthercontains a second lower speed value and a second upper speed value whichtogether define a second disallowed speed range, wherein the controlunit is operable to— determine whether the electric motor is unable toachieve the desired speed value due to a limiting condition and isrepeatedly changing between the first actual speed value that is withinthe second disallowed speed range and the second actual speed value thatis at or below the second lower speed value over the first predeterminedperiod of time, and if so, set the temporary speed limit for theelectric motor at the second lower speed value for the secondpredetermined period of time.
 8. The electric motor system as set forthin claim 7, wherein— the first disallowed speed range is associated witha first flag in the memory element, and if the first flag is not setthen the control unit ignores the first disallowed speed range; and thesecond disallowed speed range is also associated with the first flag inthe memory element, and if the first flag is set then the control unitignores the second disallowed speed range
 9. The electric motor systemas set forth in claim 7, wherein— the first disallowed speed range isassociated with a first flag in the memory element, and if the firstflag is not set then the control unit ignores the first disallowed speedrange; and the second disallowed speed range is associated with a secondflag in the memory element, and if the second flag is not set then thecontrol unit ignores the second disallowed speed range
 10. A motorcontrol system operable to control operation of an electric motor havingshaft for driving a load, the motor control system comprising: a speedsensor operable to measure an actual speed value of the electric motor;a memory element containing a first lower speed value and a first upperspeed value which together define a first disallowed speed range for theelectric motor, and further containing a second lower speed value and asecond upper speed value which together define a second disallowed speedrange; and a control unit in electrical communication with the speedsensor and the memory element, and operable to— calculate a desiredspeed value for the electric motor, wherein the desired speed value isnot within the first or second disallowed speed ranges, and to generateand send an electrical signal to cause the electric motor to attempt toachieve the desired speed value, receive the measured actual speed valueof the electric motor from the speed sensor, determine whether theelectric motor is unable to achieve the desired speed value due to alimiting condition and is repeatedly changing between a first actualspeed value that is at or below the first lower speed value and a secondactual speed value that is within the first disallowed speed range overa first predetermined period of time, wherein the first predeterminedperiod of time is approximately the time required for the electric motorto change between the first actual speed and the second actual speedbetween one time and three times, and if so, set a temporary speed limitfor the electric motor at the first lower speed value for a secondpredetermined period of time, wherein the second predetermined period oftime is approximately between twenty minutes and forty minutes,determine whether the electric motor is unable to achieve the desiredspeed value due to the limiting condition and is repeatedly changingbetween the first actual speed value that is at or below the secondlower speed value and the second actual speed value that is within thesecond disallowed speed range over the first predetermined period oftime, and if so, set the temporary speed limit for the electric motor atthe second lower speed value for the second predetermined period oftime, and at the end of the second predetermined period of time, removethe temporary speed limit.
 11. The motor control system as set forth inclaim 10, wherein the electric motor is a three-phase permanent magnetelectric motor.
 12. The motor control system as set forth in claim 10,wherein the load is a fan component of a heating and air-conditioningunit.
 13. A method of controlling an electric motor, the methodcomprising the steps of: (1) defining a first disallowed speed range forthe electric motor by storing in a memory a first lower speed value anda first upper speed value; (2) determining an actual speed value of theelectric motor; (3) calculating a desired speed value for the electricmotor, wherein the desired speed value is not within the firstdisallowed speed range, and generating and sending an electrical signalto cause the electric motor to attempt to achieve the desired speedvalue; (4) receiving the determined actual speed value of the electricmotor; (5) determining whether the electric motor is unable to achievethe desired speed value due to a limiting condition and is repeatedlychanging between a first actual speed value that is at or below thefirst lower speed value to a second actual speed value that is withinthe first disallowed speed range over a first predetermined period oftime; (6) if so, setting a temporary speed limit for the electric motorat the lower speed value for a second predetermined period of time; and(7) at the end of the second predetermined period of time, removing thetemporary speed limit.
 14. The method as set forth in claim 13, whereinthe electric motor is a three-phase permanent magnet electric motor. 15.The method as set forth in claim 13, wherein the first predeterminedtime is approximately between 20 seconds and 40 seconds.
 16. The methodas set forth in claim 13, wherein the first predetermined time isapproximately the time required for the electric motor to change betweenthe first actual speed and the second actual speed between one time andthree times.
 17. The method as set forth in claim 13, wherein the secondpredetermined time is approximately between 20 minutes and 40 minutes.18. The method set forth in claim 13, further including the steps of—defining a second disallowed speed range for the electric motor bystoring in a memory a second lower speed value and a second upper speedvalue; determining whether the electric motor is unable to achieve thedesired speed value due to the limiting condition and is repeatedlychanging between the first actual speed value that is at or below thesecond lower speed value to the second actual speed value that is withinthe second disallowed speed range over the first predetermined period oftime; if so, setting the temporary speed limit for the electric motor atthe second lower speed value for the second predetermined period oftime.
 19. The method as set forth in claim 18, wherein— the firstdisallowed speed range is associated with a first flag in the memoryelement, and the method further including the steps of allowing forsetting the first flag, and if the first flag is not set then ignoringthe first disallowed speed range; and the second disallowed speed rangeis also associated with the first flag in the memory element, and themethod further including the steps of if the first flag is set thenignoring the second disallowed speed range
 20. The method as set forthin claim 18, wherein— the first disallowed speed range is associatedwith a first flag in the memory element, and the method furtherincluding the steps of allowing for setting the first flag, and if thefirst flag is not set then ignoring the first disallowed speed range;and the second disallowed speed range is associated with a second flagin the memory element, and the method further including the steps ofallowing for setting the second flag, and if the second flag is not setthen ignoring the second disallowed speed range